Global Coastal Hazard Maps Underestimate Flood Risks For 132 Million People Due To Widespread Sea-Level Baseline Errors

Widespread errors in sea-level studies have masked the true risk to 132 million people. New research shows the ocean is already higher than maps assume.

By: AXL Media

Published: May 2, 2026, 5:45 AM EDT

Source: Information for this report was sourced from Earth.com and the University of Padova.

The Hidden Flaw In Coastal Elevation Models

A major scientific audit has uncovered a fundamental error in the baseline assumptions used to create the world's coastal risk maps. For decades, many researchers have operated under the assumption that the ocean's surface is a uniform "zero" point, but new data suggests this starting line is often set too low. Scientists from the University of Padova, led by research published in May 2026, discovered that local water levels are consistently higher than the global averages used in 385 separate hazard assessments. This discrepancy means that millions of people are already living much closer to present-day sea levels than official maps suggest, effectively shortening the window for climate adaptation and infrastructure reinforcement.

Regional Blind Spots In Southeast Asia and the Pacific

The accuracy of sea-level mapping varies significantly by geography, with the most severe errors concentrated in the Global South. While North American and European coastlines benefit from dense gravity measurements and long observational records, regions such as Southeast Asia, Africa, and Latin America rely on "rougher" baselines. In many Pacific islands and Asian deltas, corrected coastal elevations were found to be more than three feet lower than older maps indicated. This data gap is particularly dangerous in high-density areas like the Mekong Delta, which was previously estimated to be 8.5 feet above sea level but is actually closer to 2.6 feet.

The Failure Of Gravity-Based Geoid Models

The root of the mapping problem lies in the scientific reliance on the "geoid," a smooth, gravity-based estimate of the Earth’s sea-level surface. While the geoid provides a tidy mathematical reference, real-world coastlines are shaped by dynamic forces including winds, tides, ocean currents, and varying salt content. When coastal studies adopt the geoid as a "global zero," they ignore the localized "sea-surface topography" that pushes actual water levels higher. The study found that 90 percent of the papers examined failed to use any measured sea-level data at all, relying instead on these idealized models that do not reflect the physical reality of a rising and shifting ocean.